This invention relates to a process for the selection of reference marks in incremental length or angle measuring instruments, as well as to devices for the execution of this process.
In West German DE-AS 25 40 412, a system is described which includes a scale having an incremental division as well as a series of reference marks spaced along the division at fixed positions. Switching means are arranged on the scale or in the immediate vicinity of the scale in order to select and bring into operation certain selected ones of these reference marks. The disclosed switching means includes magnets and correspondingly positioned reed switches. As disclosed in this application, the magnets are used to identify selected ones of the reference marks to be put into operation, and the magnets must be physically shifted along the scale in order to position a magnet adjacent to each selected reference mark. When reference marks are selected in this manner, any one of a wide range of control processes in the incremental position measuring instrument can be triggered by means of the selected reference marks.
In addition, documents such as West German De-PS 24 16 212 and West German DE-OS 24 18 909 describe arrangements for the evaluation of each of a series of coded reference marks, each of which is allocated to a fixed position with respect to the scale. These positions are encoded on the reference marks as identification features. The reference marks are read during the measuring process and the counter state of the instrument is set, if need be, to the numerical value of the position associated with each respective reference mark as that reference mark is read.